In the scientific journal Marine Mammal Science, researchers from Cascadia Research Collective in Washington state, NOAA’s Southwest Fisheries Science Center in California, and Canada’s Department of Fisheries and Oceans identified 15 separate cases where blue whales were seen off British Columbia and the Gulf of Alaska. Four of the whales were identified as animals previously observed off the coast of California, suggesting a re-establishment of a historical migration pattern.

Researchers made this identification by comparing photographs of blue whales taken in the north Pacific Ocean since 1997 with a library of nearly two thousand photographs of blue whales off the West Coast. A positive match was determined based on pigmentation patterns in skin color and shape of the dorsal fin.

Blue whales were severely depleted during commercial whaling activities during the early 1900’s in the north Pacific and along the West Coast as far south as Baja California. Formerly large populations of blue whales in the north Pacific never rebounded after commercial whaling ended while those animals off southern California have apparently fared much better.

Scientists are still not certain exactly why blue whales are now beginning to migrate from southern California to the north Pacific Ocean although changing ocean conditions may have shifted their primary food source of krill further north.

Blue whales are thought to be the largest animal ever to have existed on earth, reaching lengths of nearly 100 feet. They were nearly hunted to extinction throughout the world and are currently listed as endangered under the U.S. Endangered Species Act and as endangered on the red list of the International Union for the Conservation of Nature. There are an estimated 5,000 to 12,000 animals remaining today, with the largest population of approximately 2,000 off the U.S. West Coast.

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